Fluid control system for selectively self-adjusting mill reduction force or interworking roll distance

ABSTRACT

A fluid control system for selectively self-adjusting mill reduction force or inter-working roll distance or roll gap comprising a variable discharging plunger pump having one port connected to a hydraulic cylinder adapted to apply pressure on working rolls in a mill and the other port connected to a fluid supply source. A servo valve is provided for deflecting deflection means in one or the other direction to control the discharge direction and discharge amount of said pump. In order to detect an existing value of mill reduction force, a fluid pressure detector is provided for electrically detecting fluid pressure in a fluid passage adapted to be connected to said hydraulic cylinder. A detector is provided for producing an electrical signal in response to the position of the ram of the cylinder. The servo valve operates in response to a result of a comparison between signals from the above-mentioned detectors and a reference value and thereby fluid is controlled so that the fluid may be in a predetermined direction and a predetermined amount so as to self-adjust mill reduction force or inter-working roll distance.

Eltrited States Paterrt Fujino et a1.

FLUID CONTROL SYSTEM FOR SELECTHVELY SELF-ADJUSTING MILL REDUCTION FORCE 0R INTERWORKING ROLL DISTANCE Inventors: Kiyoshi Fujino; Shigenobu Otsuka; Tetuo Kaichi; Takaharu Sugiyama; Koji Tamura, all of Ube, Japan Ube Industries Ltd., Yamaguchiken,.lapan Filed: Sept. 23, 1970 Appl. No.: 74,789

Assignee:

Foreign Application Priority Data Sept. 29, 1969 Japan ..44/76935 Jan. 30, 1970 Japan ..45/8905 US. Cl. ..72/8, 72/20, 72/21, 72/28 Int. Cl ..BZlb 37/10, B2lb 37/08 Field of Search ..72/8-16, 21, 19, 72/20 References Cited UNITED STATES PATENTS 6/1968 Reinhardt et al. ..72/8 12/1968 Dey et al ..72/21 X Rastelli ..72/ l 9 Herbst ..72/8

Primary Examiner-Milton S. Mehr Attorney-Woodling, Krost, Granger & Rust 5 7] ABSTRACT A fluid control system for selectively self-adjusting mill reduction force or inter-working roll distance or roll gap comprising a variable discharging plunger pump having' one port connected to a hydraulic cylinder adapted to apply pressure on working rolls in a mill and the other port connected to a fluid supply source. A servo valve is provided for deflecting deflection means in one or the other direction to control the discharge direction and discharge amount of said pump. In order to detect an existing value of mill reduction force, a fluid pressure detector is provided for electrically detecting fluid pressure in a fluid passage adapted to be connected to said hydraulic cylinder. A detector is provided for producing an electrical signal in response to the position of the ram of the cylinder. The servo valve operates in response to a result of a comparison between signals from the above-mentioned detectors and a reference value and thereby fluid is controlled so that the fluid may be in a predetermined direction and a predetermined amount so as to self-adjust mill reduction force or inter-working roll distance.

9 Claims, 5 Drawing Figures rArcmcnsms I912 I 3.693. 385 sum 2 or 3 FIG.2

PATENTEUSEPZB I972 SHEET 3 OF 3 F I G 3 a ,za 4 Potent/0- d/fferentm/ main torgae Plunger meter amplifier ampllfier motor Pump 5 6 g erenv/a/ transfo m 35 fluid pressu re detector Q q? 68 5 9 6 0 5 g F|G.4 diyj tfi l rvers.'ble| D-A l dqj kflt/a/ main ,toqzue Hanger mm enemtor counter conver a lei a ly/er o or pump 1/ pflerentia/ [(1)0 transformer A-D laid/pressure converter detector d/j/la/f/u/a feswre detector FLUID CONTROL SYSTEM FOR SELECTIVELY SELF-ADJUSTING MILL REDUCTION FORCE OR INTERWORKING ROLL DISTANCE BACKGROUND OF THE INVENTION Prior art mills are generally classified into two groups one group of which is that for self-adjusting mill reduction force and the other group of which is that for selfadjusting inter-working roll distance. Thus, a single mill has been designed to effect only one of the two types of self-adjustment functions as mentioned above which inevitably increases installation expenditure resulting in increase in cost of products obtained by such a mill. In addition, a single common oil pump has been conventionally employed for both the working and driving sides of a single mill and an oil pressure servo means has been disposed in a common oil passage connecting between the oil pump and cylinders on the opposite sides or working and driving sides of the mill. However,

in such an arrangement, mill reduction force on each side of the mill can not be adjusted independently of that on the other side of the mill. Such independent adjustment of mill reduction force on each mill side is required when working rolls on either one side of the mill have been deformed or working rolls on the opposite mill sides have been deformed by different degrees which makes reduction force and inter-working roll distance on one side different from that on the other side and then the reduction force andinter-working roll distances are to be equalized on the opposite mill sides. Furthermore, since the components of he conventional control systems for mills are mechanically driven, delay in control occurs due to inertia force in the components which makes it very difficult to obtain high quaIity products. In such a conventional control system, adjustment of mill reduction speed has been effected by adjusting the throttle of an oil circuit. Thus, in a'p'ractical operation, it has been'impossible to adjust millreduction speed in proportion to the amount of deviation of a detected value of mill reduction speed with respect to a predetermined value for such speed. Such automatic adjustment of mill reduction speed is required from the fact that when such a deviation is substantial the deviation must be eliminated as soon as possible and the adjustment must be smoothly effected by minimizing error due to inertia force at the final stage of adjustment. In other words, such adjustment is effected efficiently nd precisely in such a manner that when the deviation is great variation in the discharge amount and pressure in a pump is made great and pump discharge amount and pressure are gradually reduced when such a variation has reduced below a predetermined value in proportion to decrease in the variation. And as to self-adjustment of inter-working roll distance, in fact it has been found that a roll housing or stand is distorted upwardly as oil pressure increases. Such upward distortion of the roll housing or stand causes a predetermined or desired inter-working roll distance to be disturbed. The conventional control system has detected the inter-working roll distance based on the existing position of the ram of the cylinder in the roll housing, but a mere comparison of the detected value of the inter-working roll distance with a predetermined value of such distance would not provide any precise inter-working roll distance.

SUMMARY OF THE INVENTION Therefore, a principal object of the present invention is to provide a fluid control system forcontrolling mill reduction whereby mill reduction force or inter-working roll distance in a single mill can be selectively controlled.

Another object of the present invention is to provide a fluid control system whereby mill reduction force on the working side and driving side of a single mill can be self-adjusted independently or jointly.

A further object of the present invention is to provide a fluid control system in which no delay in control occurs in the components of said system.

A further object of the present invention is to provide a fluid control system for controlling mill reduction whereby mill reduction speed is increased in proportion to difference between a detected value of mill reduction force or inter-working roll distance and a predetermined value of such factor.

A still further object of the present invention is to provide a fluid control system for controlling mill reduction whereby deviation of inter-working roll distance from a predetermined one due to any upward distortion of a roll stand as well as variation in the position of a cylinder ram can be compensated for.

According to the present invention, the fluid control system includes a plunger pump which feeds fluid to a hydraulic cylinder cooperating with-working rolls on each of the working and driving sides of a mill and which sucks the fluid in. The pump includes deflection means for controlling the direction and amount of flow of fluid and the displacement direction and distance of the deflection means are determined by a servo valve. The servo valve is controlled by atorque motor which is adapted to drive said servo valve in response to either a result of comparison of an output signal from a detector adapted to electrically detect fluid pressure applied to said hydraulic cylinder with an output signal from mill reduction force setting means or a result of comparison of output signals from a detector adapted to electrically detect the position of the ram of said hydraulic cylinder and from said fluid pressure detector with an output signal from inter-working roll distance setting means. A deflector position detector which produces an output signal in response to the position of the deflector in the plunger pump is provided and such output signal is compared with a value obtained from the comparison made in the manner as mentioned above and introduced into an electrical input of the torque motor. Thus, the torque motor controls the plunger pump in such a manner that fluid pressure in the hydraulic cylinder or the position of the ram of the cylinder may be maintained at a predetermined pressure or in a predetermined position.

The above and other objects and attendant advantages of the present invention will be more clearly apparent to those skilled in the art from a reading of the following description of the invention referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a four high mill and a preferred form of fluid control system for selectively controlling working pressure or rolling reduction in said mill according to the present invention;

FIG. 2 is a view showing a variable discharge radial plunger pump employed in said fluid control system in section and electro-mechanical servo means for controlling the discharge of said pump together with an electrical circuit for said servo means;

FIG. 3 is a view showing specific relationship between principal components of said fluid control system when the control system is operated for automatically adjusting reduction force in said mill;

FIG. 4 is a view showing specific relationship between principal components of said fluid control system when the system is operated so that a predetermined distance may be obtained between working rolls in said mill; and

FIG. is a schematic diagram of a modified form of fluid control system employing an axial plunger pump according to the present invention showing said pump in section.

PREFERRED EMBODIMENTS OF THE INVENTION Referring to FIG. 1 of he accompanying drawings in which a four high mill is schematically shown, the working side of the mill is generally indicated by I on the left hand side of the Figure whilst the driving side of the mill is generally indicated by [I on the right hand side of the same Figure. These sides of the mill are substantially identical in construction and operation. The mill generally comprises a roll stand or housing 1 in which a pair of working rolls 2 and 3 and a pair of backing-up rolls 4 and 5 which back up the working rolls, respectively are provided. The working rolls 2 and 3 are supported at the opposite ends by pairs of chocks 6, 6' and 7, 7 respectively. The backing-up rolls 4 and 5 are supported at the opposite ends by pairs of chocks 8, 8 and 9, 9', respectively. These rolls and chocks are mounted on carriages 10 and 10' which are in turn are supported on rams l1 and 11' in hydraulic cylinders 12 and 12', respectively. The cylinders 12 and 12' are supplied with oil through their respectively associated conduits 28 and 28' which are in turn connected to their respectively associated oil supply sources and as a result, the roll 2 applies a predetermined pressure on the roll 3 and the rolls are maintained at a predetermined spaced relation therebetween by means of the rams 11 and 11' which are urged toward these rolls under the hydraulic pressure supplied into the cylinders. Mounted on the hydraulic cylinders 12 and 12', respectively, are digital detectors 14 and 14 which electrically detect the position of the working rolls or thedistance between the working rolls based on the oil pressure supplied into the cylinders. These detectors are signal generators adapted to convert a vertical displacement distance of arms 13 and 13' which are respectively mounted on the rams 11 and 11' into a digital signal. The signal generators may be constituted by conventional digital type pulse generators.

The conduit 28 and 28' are connected to their respectively associated control systems of which detailed description will be made hereinbelow and to which the present invention directs. Since the control systems on the opposite sides of the four high mill are identical with each other, detailed description will be made on only the system on the working side of the mill herein and therefore, the parts of the control system on the driving side of the mill which correspond to those on the working side are assigned the same reference numerals as those of the working side with addition of primes thereto, respectively.

The fluid control system generally comprises a radial plunger pump 16 which 'has an. electro-oil pressure servo mechanism which automatically regulates the discharge amount of the pump. The pump 16 has a port A (FIG. 2) connected to the conduit 28 and another port B connected to an oil tank 24. The port B is normally employed as a suction port, but in order that the port B may be employed as a discharge port, the port B is provided with a relief valve 21 which is adapted to set the discharge pressure at the port B when employed as the discharge port to a value on the order of IO kg/cm The fluid control system further comprises a low pressure pump 17 in the form of gear pump which is connected to a reducing valve 18 which is in turn connected through check valves 26 and 23 to the ports A and B of the pump 16, respectively. The output of the pump 17 is also employed for controlling the discharge direction and amount of the radial plunger pump 16. The reducing valve 18 serves to maintain pressure for controlling the discharge direction and amount of the pump 16 at a predetermined value such as 15 kglcm for example. As shown in FIG. 2, the pump 17 is disposed within the housing of the pump 16.

An unloading electromagnetic valve 19 is connected to a branch conduit leading from he conduit 28 and an accumulator 30 is connected through an electromagnetic valve 31 and a stop valve 32 in a branch conduit leading from the conduit 28 to the conduit. The stop valve 32 is in turn connected through a stop valve 33 to a reservoir 24. The accumulator 30 serves as a cushion in the event that the operation of the pump 16 fails to follow any abrupt change in the thickness of material to be rolled when mill reduction pressure is controlled. For example, if the material to be rolled is urged into the space between the working rolls 2 and 3 when these rolls are in contact with each other the accumulator 30 serves as a cushion. The valve 31 is so designed that the valve is opened when the control system is operated for controlling mill reduction pressure and closed when the control system is operated for controlling the position of the working rolls or inter-roll distance.

The conduit 28 is also connected to a relief valve 27 which is in turn connected to the reservoir 24. The relief valve 27 serves to limit the upper limit of oil pressure required for reducing the material at the port A in the radial plunger pump 16 which normally acts as the discharge port of the pump. The maximum oil pressure for reducing the material may be on the order of 21 kg/cm for example.

The conduit 28 is also connected through a stop valve in a branch conduit leading from the conduit to a pressure gauge 25 disposed in the same branch conduit and the pressure gauge gives a visual reading of the oil pressure in the conduit 28.

Details of the radial plunger pump 16 and its associated electro-fluid servo mechanism are shown in FIG. 2.

The radial plunger pump 16 comprises a housing 41, a cylindrical rotor 42 rotatably supported on a transverse pintle within the housing, a plurality of plungers 44 slidably extending radially through corresponding radial bores in the rotor, a slide ring 45 along the inner surface of which the plungers are guided and an annular slide block 46 for moving the slide ring between its eccentric position and equlibrium position. The housing 41 is closed at the opposite ends by enclosure plates 41a and 49. The cylindrical rotor 42 has a pair of axial fluid passages extending in opposite directions from its center along the axis of the rotor and the passages are closed at the inner ends and separated from each other and open at the outer ends which provide the abovementioned ports A and B, respectively. In FIG. 2, the fluid passages are shown by the radially extending dotted lines for the purpose of illustration. The rotor 42 is rotated at a controlled speed in the arrow direction by an electric motor (see FIG. 1) which also rotates the gear pump 17. The slide block 46 are provided at the opposite ends with stroking piston portions 47 and 48 which are adapted to slide along the inner surface of the housing 41 in a fluid tight relation therewith. The piston portions are deflected under the influence of control fluid from control fluid passages 53 and 54 so as to cause the slide block rightwards or leftwards.

The plunger pump may be used which has been sold under the trade name Oilgear type Pump by The Oilgear Company in U.S.A. and the detailed structure and operation of such pumps has been well known. The outline of the operation of the plunger pump is as follows: When the slide block is in its equilibrium position oil will not be discharged out of or sucked in the port A or B even if the cylindrical rotor continues to rotate. When the slide block 46 is deflected rightwards as seen in FIG. 2 by the piston portion 47, the slide ring 45 is rendered eccentric with respect to the rotor 42 as shown in FIG. 2 whereby oil is sucked into the port B and discharged out of the port A. The greater the eccentricity of the slide ring is, the greater the amount of v oil to be sucked into the the port B is and the greater the amount of oil to be discharged out of the port A is. On the contrary, when the slide block 46 is deflected leftwards by the piston portion 48, oil is sucked into the port A and discharged out of the port B. When oil is to be supplied to the port B the oil is supplied from the gear pump 17 through a passageway 52, the reducing valve 18 and check valve 23 to the port B. When discharged out of the port B, the oil is returned through the relief valve 21 to the reservoir 24.

Control fluid which displaces the slide block rightwards or leftwards is supplied from the pump 17 through the passageway 52 and is selectively communicated with a passageway 53 or 54 by the servo valve 22. The servo valve 22 includes a valve body 50 having passageways 52', 53' and 54 which are in communication with the passageways 52, 53 and 54 and a sliding member 51 which communicates between the passageways 52 and 53' or between the passageways 52' and 54' or blocks oil flow between the passageway 52' and passageways 53 and 54'.

A torque motor 55 is provided for sliding the sliding member 51 toward the passageway 53' or 54'. The torque motor comprises an armature 55a rotatable about the axis of a pivot X and field coils 55b and 55c.

One or theother free end of the armature 55a pivotally supports an extension 51a of the sliding member 51 thereon. When one of the field coils of the field coil 55b is excited, the armature is rotated in the clockwise direction in FIG. 2 thereby to displace the sliding member 51 so that the sliding member may communicate between the passageways 52 and 53' or between the passageways 52 and 53. On the other hand, when the other field coil 550 is excited, the armature is rotated in the counter-clockwise direction in FIG. 2 thereby to displace the sliding member 51 so that the sliding member may communicate between the passageways 52' and 54' or between the passageways 52 and 54. In this way, either the piston portion 47 or 48 of the radial plunger pump 16 is supplied with control oil from the pump 17 through the servo valve 22. The amount of control oil to be supplied varies depending upon the inclination angle of the armature and arcordingly, displacement distance of the sliding member and the supply amount of control oil determines the amount of oil to be discharged out of the port A or B. And when neither the field coil 55b nor 550 of the torque motor 55 is excited, the armature 55a is maintained in its neutral position as shown in FIG. 2, and accordingly, the sliding member of the servo valve 22 is so positioned that fluid communication between the passageways 52' and 53 or 54' is blocked. It will be understood that in order to return the slide block of the pump 16 from any deflected position to the equilibrium position the fieldcoil other than that previously employed in deflecting the slide block must be excited. As the result that either the piston portion 47 or 48 is supplied with control oil, oil within the other piston portion which is not supplied with the control oil is allowed to return through the passageways53' and 54' of the servo valve which are then open to the reservoir 24. When the servo valve 22 is blocking between all the passageways, the oil from the gear pump 17 flows through the reducing valve 18 and relief valve 20. Since the relief valves 20 and 20' are connected through a cooler 39 to the reservoir 24, the oil which has passed through the relief valve 20 is cooled through the cooler 39 before it returns to the reservoir'24. A check valve 40 is connected to the cooler 32 in parallel to the latter and the check valve allows oil to flow easily to the reservoir 24 even if the cooler 39 has a small capacity. The check valve 40 also serves as a safety valve in the event that the flow of oil is blocked due to any cause.

An oil pressure detector 35 is provided for converting oil pressure within the conduit 28 into a corresponding electrical signal. The detector is shown in the form of a differential transformer 57. The transformer comprises a core 57a and primary and secondary windings 57b and 570 and the secondary winding includes two coils having the same number of turns and differentially connected to each other. The core 57a is mechanically secured to a Bourdons tube 36 which is in turn connected to the conduit 28. Accordingly the Bourdons tube 36 is extended or retracted in response to oil pressure within the conduit 28 whereby the core 57a is displaced so as to produce in the secondary winding 570 an electrical signal having a polarity and amplitude corresponding to a particular oil pressure which is then present in the conduit 28. The primary winding 57b of the transformer is connected to an output winding 34b in a power transformer 34. The secondary winding 57c is connected through a potentiometer 61 which will be described hereinbelow to a Q input of a differential amplifier 59. A detector such as a differential transformer 56 is provided for detecting the position of the slide block 46. The differential transformer 56 comprises a core 56a and primary and secondary windings 56b and 56c. The secondary winding 560 includes two differential coils similar to those employed in the secondary winding of the transformer 57. The primary winding 56b is connected to an output winding 34b of the power transformer 34. The core 56a is connected to the slide block 46 by means of an arm 46a which is slidable through the wall of the housing 41 and enclosure plate 49 and extends through the housing in a fluid-tight relation to the latter. Accordingly, when the slide block 46 is in the neutral position, no output is produced in the winding 56c of the transformer 56. However, when the slide block 40 is deflected leftwards or righwards from the neutral position as seen in FIG. 2, an output is produced in the winding 56c having a polarity and amplitude corresponding to the direction and distance of such deflection. The winding 560 is connected to P input of a differential amplifier.

The differential amplifier 59 detects difference between voltages of signals entering inputs P and Q and amplifies the detected differential voltage. An output of the amplifier is connected to an input of a main amplifier 60 outputs of which are in turn connected to the coils 55b and 550 of the torque motor 55. Thus, either the coil 55b or 55c is excited depending upon difference between input voltages and amplitudes, but when the differential voltage is zero, neither thecoil 55b nor 550 is excited.

In order to set oil pressure within the conduit 28 at a predetermined value, an oil pressure control circuit 58 comprising potentiometers 61 and 62 and a current restricting resistor 63 is provided. The potentiometers 61 and 62 and resistor 63 are in series connected to each other with one end of the potentiometer 61 connected to the neutral point of the winding 34b in the power transformer 34 and one end of the resistor 63 connected to a tap of the coil 34b. The wiper 61a of the potentiometer 61 is connected to one of the output terminals of the coils in the differential transformer 57 while the other output terminals of the differential transformer coils and the above-mentioned one end of the potentiometer 61 are connected to the Q input of the differential amplifier. The wiper 61a of the potentiometer 61 cooperates with the corresponding wiper of a similar potentiometer in the oil pressure controlling circuit on the driving side of the mill (not shown). Thus, it will be appreciated that the two potentiometers simultaneously vary oil pressures in the conduits 28 and 28' on the working and driving sides of the mill in the same direction and by the same degree. It will be also understood that the potentiometer 62 serves to independently set oil pressure in the conduit 28 on the working side and the similar potentiometer has the identical function on the driving side. Thus, it is apparent that when the potentiometer 62 and the other sililar potentiometer (not shown) are regulated to the same set value oil pressure in the conduits 28 and 28' can be set at the same value as desired only by the potentiometer 61.

In order to maintain the working rolls in a desired spaced relation to each other, an inter-working roll distance controlling circuit is provided. The controlling circuit comprises a working roll position or distance setting device 66 for generating a digital signal corresponding to the desired distance between the working rolls, a working roll position or distance detector 14 attached to the oil cylinder 12 for electrically detecting the displacement of the ram 11 of the cylinder, the above-mentioned oil pressure detector 35 for detecting oil pressure in the conduit 28, an analog digital converter for converting analog signals from the detector into digital signals and a comparator 67 for comparing the sum of a digital signal from the working roll distance detector 14 and a digital signal from the converter 100 against a digital reference signal from the working roll distance setting device 66. In the illustrated embodiment, the working roll position detector 14 comprises an arm 13 attached to the ram 11 and a mechanical electrical converter (not shown) for converting a vertical displacement of the arm 13 into a digital signal. The converter may be a conventional counter. The comparator 67 is a digital reversible counter which produces a counting pulse representing any deviation of the sum of the digital signal from the working roll distance detector and that from the converter with respect to the digital reference signal. In the present invention it is important that the reference signal from the setting device is compared with not only the digital signal from the detector 14, but also with the digitalized oil pressure response signal. The reason is that the distance between the working rolls tends to deviate from a desired or set value subject to any upward distorsion of the roll housing by the action of oil pressure and such deviation of the inter-roll distance is detected by the detector 35 as a variation in oil pressure. Thus, according to the present invention, the output of the digital counter 67 contains both a primary deviation of the inter-working roll distance or of the ram 11 of the cylinder 12 and a secondary deviation caused by any upward distortion of the roll housing.

The controlling circuit also includes a digital analog converter 68 connected to the output of the digital counter 67. The converter 68 includes a position controlling command potentiometer 69 the opposite ends of which are connected to two taps of the output winding in the power transformer 34, respectively and the wiper 69a of which is connected to one of Q input terminals of the differential amplifier 59. Thus, the radial plunger pump is so controlled that an analog signal from the digital analog converter 68 which represents any deviation of the inter-roll distance from the predetermined or desired inter-roll distance is applied to the Q inputs of the amplifier 59 and the polarity (which is determined depending upon whether the detected inter-roll distance is greater or smaller than the preset distance) and the amplitude of the analog signal cause oil to be discharged out of the port A of the radial plunger pump 16 or to be sucked into the port A of the same pump thereby to compensate for the deviation.

According to the present invention, in order that mill reduction force or inter-working roll distance may be selectively maintained at a preset value, the fluid control system includes a selecting means which comprises a relay coil (not shown) and relay contacts 64 and 65.

The relay contacts 64 are disposed between the output terminals of the differential transformer 57, the wiper 61a and the input of the differential transformer 59, respectively. And the raly contacts 65 are disposed between the output of the transformer 57 and the input of the analog digital converter 100 and between the wiper 69a of the potentiometer 69 in the digital analog converter 68 and the Q input of the difierential amplifier 59, respectively. The relay contacts 64 are normally open contacts while the realy contacts 65 are normally closed contacts. Accordingly, when the relay coil is in its deenergized condition, the fluid control system serves to self-adjust the inter-working roll distance and on the other hand, when the relay coil is in it energized condition the fluid control system serves to self-adjust mill reduction force.

In operation, assuming that the fluid control system is operated for self-adjusting mill reduction force, the relay coil is first energized to close the normally open realy contacts 64 and open the normally closed relay coils 65. The oil pressure setting circuit 58 sets its potentiometer 61 at a value corresponding to a desired mill reduction force (FIG. 3). In the system as shown in FIG. I, the stop valve 32 opens and the stop valve 33 closes. And the motor is rotated thereby to continuously rotate the roter 42 of the radial plunger pump 16 and the gear pump 19. Then, when a workpiece or strip is fed between the working rolls 2 and 3, the strip causes oil pressure in the conduit 28 to rise, but it is assumed that the value of increased oil pressure is still below a preset value. This generates a voltage in the output winding 57c of the differential transformer 57 which is 180 out of phase with respect to a voltage at the potentiometer 61. The sum 0) of the output winding voltage and potentiometer voltage is applied to the Q input of the differential amplifier 59 and the sum voltage is then amplified through the amplifier 59. The amplified voltage is further amplified through the main amplifier 60. The thus amplified voltage from the output of the amplifier 60 is applied to the torque motor 55 to rotate the armature of the motor in the clockwise direction about the pivot X thereby to displace the slide block 46 rightwards as seen in FIG. 2 resulting in discharge of oil out of the port A of the pump 16. And when the slide block 46 is displaced rightwards as seen in FIG. 2, a signal corresponding to the rightwards displacement of the slide block is generated in the output of the coil 56c in the differential transformer 56 to be applied to the P input of the differential amplifier 59. When oil pressure in the conduit 28 rises in response to discharge of oil out of the port A, a signal applied to the Q input of the difierential amplifier 59 approaches zero, but difference between the voltage at the P input (which is then greater than the Q input voltage) and that at the Q input is amplified through the amplifier 59 and further amplified through the main amplifier 55 thereby to imparts the aramature 55a a pivotal move ment in the counter-clock direction as seen in FIG. 2 and the output of the differential transformer 56 approaches zero. In this way, when the sum of the voltages at the P and Q inputs of the differential amplifier 59 approaches zero (then both the P input voltage and the Q input voltage are zero), the torque motor is deenergized and the slide block 46 of the radial plunger pump 16 remains in the neutral position to terminate discharge of oil out of the port A. At this time, oil pressure in the conduit 28 becomes equal to a value set for the oil pressure setting circuit 58. In fact, when microscopically viewed, the'Q input voltage at the amplifier 59 becomes equal to the P pointvoltage at theamplifier 59 which originally came from the transformer 56 which detects the position of the slide block 46 as oil pressure in the conduit 28 rises, and then torque motor 55 assumes the neutral position. However, oil continues to discharge out of the pump 16 to make the Q input voltage from the amplifier 59 smaller than the P input voltage whereby the armature of the torque motor 55 is rotated in the counter-clock direction and the slide block 46 of the pump 16 is displaced towards the neutral position. When oil pressure in the conduit 28 reaches a preset value as the above procedure is repeated,'the rotor of the radial plunger pump 16 assumes the neutral position and maintains the position.

When oil pressure in the conduit 28 exceeds the preset value due to variation in the strip thickness and/or any other factor or factors, a deviation voltage having the polarity opposite to that of the previous deviation voltage is applied to the 0 input of the differential amplifier 59 whereby the armature 55a of the torque motor 55 is rotated in the counter-clockwise direction and the slide block 46 of the pump 16 is displaced leftwards as seen in FIG. 2 resulting in sucking of oil into the port A of the pump 16 and discharge of oil out of the port B of the same pump. When the oil pressure in the conduit 28 again reaches the preset value as the oil pressure is continuously reduced and the slide block is continuously returned toward the right hand position, the pump assumes the neutral position. It will be understood that when the potentiometers 62 in the mill reduction force setting circuits are vset at the same value on both the working and driving sides of the four high mill setting force will be the same on both the sides of the mill. However, when working roll or rolls on one side of the mill have been deformed or the working rolls on the opposite sides of the mill have been differently deformed resulting in difference in reduction force on the opposite sides of the mill, in order to equalize the reduction force on the opposite sides of the mill, it may be desired to provide a differential pressure. In such a case, he potentiometers 62 on the working and driving sides of the mill are independently adjusted so as to provide different reduction forces on the opposite sides of the mill, respectively.

When the fluid control system of the invention is operated for self-adjusting the inter-roll distance on the working side of the mill to a desired or preset value, the relay coil is deenergized to close the relay contacts 65 and open the relay contacts 64. The roll position setting device 66 is set so that the desired or preset inter-roll distance may be obtained (FIG. 4). The detector 14 generates a digital signal in response to the existing inter-roll distance and the oil pressure detector 35 generates a digital signal in response to an upward distortion of the roll stand or housing through the analog digital converter 100. These signals are then compared with a preset signal from the position setting device 66 through the reversible counter 67. A signal representing difference between these signals exits in the form of a digital output signal out of the counter 67. The signal is then converted into an analog signal through the digital analog converter 68. When the signal from the detector M and that from the converter 106 are found as exceeding over their respectively preset values, an output signal from the converter 68 has one polarity. On the contrary, when the abovementioned two signals are found as being below their respectively preset values, the signal from the converter 68 has the opposite porality. The output signal is then applied to the amplifiers 59 and 60. Thus, the torque motor 55 is rotated in the clockwise or counterclock direction depending upon the porality of the output signal from the converter 68 so as to cause oil to be discharged out of the port A of the radial plunger pump 16 and to be sucked into the port B of the same pump thereby to self-adjust the position of the working rolls or the inter-roll distance to a preset or desired one. It is to be particularly noted that variation in oil pressure in the conduit 28 is partially caused by a deviation in the inter-roll distance from a preset distance due to an upward distortion of the roll stand or housing I and accordingly, if a signal from the oil pressure detector is applied to the roll position control means, the inter-roll distance can be brought to a desired or preset value more precisely.

Referring now to FIG. of the accompanying drawings, an alternate embodiment of the invention is shown and in the alternate embodiment the axial plunger pump 16 is employed in place of the radial plunger pump of FIG. 2. The axial plunger pump 16 comprises a housing 72, a cylindrical barrel 76 attached to a portion of the inner wall surface of the housing, a series of pistons 77 slidably fitted in aligned axial bores formed in the barrel, an inclining block facing and axially aligned with the barrel 76 and connecting rods 78 connecting between the pistons 77 and inclining block 73. One end of each of the connecting rods 78 is formed in the shape of a ball 79a and the ball end is received in a recess formed in the opening of the respectively associated piston 77 while the other end of each of the connecting rods is also formed in the shape of a similar ball 7% and received in an annular recess 820 formed in a receptacle 82 for the inclining block 73. The axial barrel bores in which one set of pistons are received open into the port A which extends through the housing wall and a portion of the barrel wall while the other axial bores in which the other set of pistons are received open into the port 13 which extends through the housing wall and a portion of the barrel wall. The receptacle 82 for the inclining block 73 is mounted on a driving shaft by means of a universal ball joint 75. The shaft 74 axially extends through the housing 72 and barrel 76 with one end supported in a portion of the housing wall by means of a bearing 74a and the other end supported in another housing portion by means of a bushing 74b. The extreme end of the other end of the shaft 74! has the motor 15 connected thereto which motor is also connected to the low pressure oil pump 17. A slide block 30 is provided for disposing the inclining block relative to the axis of the shaft 14. The slide block 80 is attached to a piston rod 71 in an oil cylinder 70 mounted on the outer wall of a housing 72 (which rod slidably extends through the call of the housing and displaces in a plane parallel to the axis of the shaft 74 upon movement of the piston rod 71. The inclining block 73 has a radial ear having a ball head $1 received in a recess formed in the slide block 80. Thus, the ball head and recess cooperate in forming a universal joint which connects between the inclining block and slide block. The oil cylinder is connected through conduits 53 and 54 to a servo valve 22 which has a construction similar to that of the corresponding valve as shown in FIGS. 1 and 2. The piston rod 71 in the oil cylinder 70 is connected to the armature of the differential transformer 56 which constitutes a position detector for the slide block or inclining block. In the embodiment as shown in FIG. 5, upon operation of the servo-valve, oil is discharged outof either the conduit 53 or 54 so as to displace the slide block rightwards or leftwards thereby to incline the inclining block 73 toward or away from the barrel 76 at an angle other than right angles with respect to the axis of the shaft 74. Such inclination of the inclining block discharges oil out of either the port A or B so that self-adjustment of mill reduction force or inter working roll distance can be effected in the same manner as mentioned in connection with the preceding embodiment.

Although two preferred embodiments of the present invention have been described and illustrated herein, it is to be understood that these are illustrative in nature and not to be necessarily limiting upon the scope of these teachings in their broader aspects. Many additional variations within the scope of the appended claims will occur to those skilled in the art.

What is claimed is:

l1. In a fluid control system for controlling mill reduction in a mill having hydraulic cylinders on the working and driving sides of the mill in pressure applying relation to working rolls in said mill, comprising variable discharge plunger pump means for supplying said hydraulic cylinders with fluid, respectively, said pump means including deflection means for stopping flow of fluid from or to ports in a neutral position and for discharging fluid from one port and sucking in fluid at another port when said deflection means is in one deflected position or discharge fluid from said other port and suck in at said one port when said deflection means is in the other deflected position; a fluid pressure detector for electrically detecting fluid pressure at said one port of the pump means; an inter-working roll distance detector for electrically detecting the position of the ram in each of said hydraulic cylinders; reduction force setting means for producing a preset signal corresponding to a predetermined value at said one port of the pump means; inter-working roll distance setting means for producing a preset signal required for predetermining the position of the ram in each of said hydraulic cylinders; a deflection means for producing a position signal in response to the position of said deflection means of said pump means; servo means including a servo valve for displacing said deflection means of the pump means in a required direction and by a required distance and a torque motor for operating said servo valve; a differential amplifier having inputs adapted to be supplied with a signal S3 from said deflection means and a signal selected from a differential signal (8,) obtained from said reduction force setting means and a signal from said pressure detector and a differential signal (8,) obtained from said interworking roll distance detector, outputs of said differential amplifier being connected to inputs of said torque motor; and selecting means for selecting either said firstimentioned signal orisaid second-mentioned differential signal.

2. A system as set forth in claim 1, in which said plunger pump means is a radial plunger pump and said deflection means is a slide block which is eccentric with respect to the axis of a rotor of said pump.

3. A system as set forth in claim 1, in which said plunger pump means is an axial plunger pump and said deflection means includes an inclining block engaged by said plunger and having a receptacle which receives said block in a rotational engagement relation with the block and a slide block for inclining said receptacle at a required angle with respect to the axis of said pump.

4. A system as set forth in claim 1, in which said fluid pressure detector comprises a differential transformer including a primary winding connected to an AC source, two secondary windings having the same umber of turns and differentially connected to each other, an armature to be magnetically linked to said primary and secondary windings and a Bourdons tube mechanically connected to said armature for extending or retracting in response to said fluid pressure.

5. A system as set forth in claim 1, in which said reduction force setting means includes first potentiometers each one disposed on the working and driving sides of said mill and each having cooperating windings for displacement in the same direction and by the same distance.

6. A system as set forth in claim 5, in which said reduction force setting device includes second potentiometers disposed on said working and driving sides of the mill to be independently adjusted of each other and said last-mentioned potentiometers are in series connected to said first potentiometers. 1

7. A system as set forth in claim 1, in which said deflection means position detector comprises a differential transformer consisting of a primary winding connected to an AC source, two secondary windings having the same number of turns and differentially connected to each other and an armature to be magnetically linked to said primary and secondary windings said armature being displaceable in response to any displacement of said deflection means.

8. A system as set forth in claim 1, in which said inter-roll distance setting means is a digital pulse generator for producing a digital reference signal corresponding to said required inter-roll distance and said inter-roll distance detector is a digital pulse generator for producing a digital signal corresponding to the position of the ram or piston of said cylinder, said output windings of the' fluid pressure detecting differential transformer being connected to an analog digital converter on the output of which a digital signal corresponding to the output signal of said transformer is produced.

9. A system as set forth in claim 8, in which said system further comprises a comparator whereby a digital signal from said first-mentioned pulse generator is compared with a digital signal from said second-mentioned pulse generator and with a digital signal from said analogdigital converter, the output of said converter being connected to said digital-analog converter. 

1. In a fluid control system for controlling mill reduction in a mill having hydraulic cylinders on the working and driving sides of the mill in pressure applying relation to working rolls in said mill, comprising variable discharge plunger pump means for supplying said hydraulic cylinders with fluid, respectively, said pump means including deflection means for stopping flow of fluid from or to ports in a neutral position and for discharging fluid from one port and sucking in fluid at another port when said deflection means is in one deflected position or discharge fluid from said other port and suck in at said one port when said deflection means is in the other deflected position; a fluid pressure detector for electrically detecting fluid pressure at said one port of the pump means; an inter-working roll distance detector for electrically detecting the position of the ram in each of said hydraulic cylinders; reduction force setting means for producing a preset signal corresponding to a predetermined value at said one port of the pump means; inter-working roll distance setting means for producing a preset signal required for predetermining the position of the ram in each of said hydraulic cylinders; a deflection means for producing a position signal in response to the position of said deflection means of said pump means; servo means including a servo valve for displacing said deflection means of the pump means in a required direction and by a required distance and a torque motor for operating said servo valve; a differential amplifier having inputs adapted to be supplied with a signal S3 from said deflection means and a signal selected from a differential signal (S1) obtained from said reduction force setting means and a signal from said pressure detector and a differential signal (S2) obtained from said interworking roll distance detector, outputs of said differential amplifier being connected to inputs of said torque motor; and selecting means for selecting either said first-mentioned signal or said second-mentioned differential signal.
 2. A system as set forth in claim 1, in which said plunger pump means is a radial plunger pump and said deflection means is a slide block which is eccentric with respect to the axis of a rotor of said pump.
 3. A system as set forth in claim 1, in which said plunger pump means is an axial plunger pump and said deflection means includes an inclining block engaged by said plunger and having a receptacle which receives said block in a rotational engagement relation with the block and a slide block for inclining said receptacle at a required angle with respect to the axis of said pump.
 4. A system as set forth in claim 1, in which said fluid pressure detector comprises a differential transformer including a primary winding connected to an AC source, two secondary windings having the same umber of turns and differentially connected to each other, an armature to be magnetically linked to said primary and secondary windings and a Bourdon''s tube mechanically connected to said armature for extending or retracting in response to said fluid pressure.
 5. A system as set forth in claim 1, in which said reduction force setting means includes first potentiometers each one disposed on the working and driving sides of said mill and each having cooperating windings for displacement in the same direction and by the same distance.
 6. A system as set forth in claim 5, in which said reduction force setting device includes second potentiometers disposed on said working and driving sides of the mill to be independently adjusted of each other and said last-mentioned potentiometers are in series connected to said first potentiometers.
 7. A system as set forth in claim 1, in which said deflection means position detector comprises a differential transformer consisting of a primary winding connected to an AC source, two secondary windings having the same number of turns and differentially connected to each other and an armature to be magnetically linked to said primary and secondary windings said armature being displaceable in response to any displacement of said deflection means.
 8. A system as set forth in claim 1, in which said inter-roll distance setting means is a digital pulse generator for producing a digital reference signal corresponding to said required inter-roll distance and said inter-roll distance detector is a digital pulse generator for producing a digital signal corresponding to the position of the ram or piston of said cylinder, said output windings of the fluid pressure detecting differential transformer being connected to an analog - digital converter on the output of which a digital signal corresponding to the output signal of said transformer is produced.
 9. A system as set forth in claim 8, in which said system further comprises a comparator whereby a digital signal from said first-mentioned pulse generator is compared with a digital signal from said second-mentioned pulse generator and with a digital signal from said analog-digital converter, the output of said converter being connected to said digital-analog converter. 